Organic fluorine compounds and specifically perfluoroketones (PFKs) are suitable insulation gases for electrical apparatus, such as medium-voltage or high-voltage switchgears. The ketones can be described by the number of carbon atoms in their main chain, for example as C5, C6, or C7 indicating that 5 or 6 or 7 carbon atoms are present in their main chain. Gas mixtures containing PFKs are preferred over pure SF6 and over SF6 mixtures due to their much lower global warming potential.
PFK mixtures are also relevant as replacement gases for air-insulated converter stations having the benefit of increased dielectric strength without the need to increase operating pressure and without much adverse environmental impact. This is of particular relevance for air-insulated converter stations. As such stations need to be accessible by humans and as they are not leakage-free, they cannot be filled with SF6. Consequently distances between live parts must be chosen to be compatible with air insulation leading to a comparatively large footprint of the station. The use of PFK/carrier gas mixtures has the potential of reducing the footprint of large air-insulated stations substantially. Another advantage of the use of PFK/carrier-gas mixtures is their non-toxicity and reduced or negligible environmental impact.
Contrary to the use in for example hermetically sealed switches and the like, when used for rooms or other enclosures of large volume any PFK/carrier gas mixtures will require more often filling or replenishing. Basis for such operations is an accurate measurement of the PFK content in the room atmosphere, in particular room air, on an essentially continuous basis.
Up to now perfluoroketones have mainly been used as refrigerants, heat transfer fluids or fire extinguishing media. There are devices available on the market that address sensing of this class of substances. For example, the company Bacharach offers a room monitor (HG-halogen gas monitor/leak monitor for refrigerant gases including the PFK C6 named Novec™ 649) which is based on an MIR (mid-infrared) absorption measurement. Further portable FTIRs (Fourier-transform infrared) spectrometers are available commercially for refrigerant leak detection, e.g. the MIRAN from the company Thermo Scientific™.
Room monitoring systems using several infrared sensors for refrigerant leaks are known for example from the brochure “Mechanical Equipment Rooms” by Honeywell™, 2011. The system described includes a plurality of different sensors connected to a controller. The controller has a relay side used to activate or deactivate alarms, vents, machinery etc.
The invention starts from JP S57 100388 which discloses an infrared laser beam for monitoring combustible or explosive gas in a semiclosed space, such as an underground market, and to shut down leakage of the gas and eventually to ventilate it out of the semiclosed space.
US 2003/0235026 discloses a converter station housed in a closed multistory building. The converter station is equipped with electrical apparatuses that are encapsulated and SF6-gas-insulated or are air-insulated.